That really depends. In your case, the answer depends on where your technical interests lie. Certainly, the MCSE (and later, the MCTS and MCITP credentials for Windows Vista that should probably start showing up in the second half of 2007) is a logical next step. After that, your technical interests will probably help you decide whether specializing in something like databases, information security, or messaging makes sense, or if Cisco and network infrastructure topics might be of greater interest.
If you can tell me more about what you do on the job, and what kinds of technology areas you find particularly interesting or appealing, I can probably do a better job of helping you put together a medium-term career development plan -- because that's really what you're asking for, whether you know it or not!
Thanks for posting, and good luck with your career development efforts.
This was first published in March 2006